As described in the literature, p-benzobisoxazole and p-benzobisthiazole polymers can be synthesized with inherent viscosities of up to 31 dl/g. These polymers possess high thermooxidative stability and, because of their all-para, rod-like character, they are capable of forming liquid crystalline phases in concentrated solutions of methanesulfonic acid. Ultra-high strength, high modulus fibers possessing a high degree of oriented, crystalline character can be obtained from these solutions. However, attempts to cast strong films from the methanesulfonic acid solutions have been unsuccessful. It has been possible to obtain only very brittle films. Articulated p-benzobisoxazole and p-benzobisthiazole polymers which contain a limited number of diphenoxybenzene segments can be synthesized with inherent viscosities as high as 12 dl/g being recorded (See my joint U.S. Pat. No. 4,229,566). These are also capable of forming liquid crystalline phases in methanesulfonic acid and can be cast into strong films from that solvent. However, the presence of the diphenoxybenzene segments, while improving the film-forming properties of the p-benzobisoxazole and p-benzobisthiazole polymers, also significantly decreases the thermooxidative stability of the polymers.
It is a principal object of this invention, therefore, to provide thermooxidative stable articulated p-benzobisoxazole and p-benzobisthiazole polymers which can be used to fabricate films and laminates having high strength and outstanding thermooxidative stability.
Another object of the invention is to provide articulated p-benzobisoxazole and p-benzobisthiazole polymers containing 3,3'-biphenyl and 2,2'-bipyridyl structures.
A further object of the invention is to provide a process for preparing the articulated p-benzobisoxazole and p-benzobisthiazole polymers containing 3,3'-biphenyl and 2,2'-bipyridyl structures.
Still another object of the invention is to provide films prepared from articulated p-benzobisoxazole and p-benzobisthiazole polymers containing 3,3'-biphenyl and 2,2'-bipyridyl structures.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.